MACRORADIOGRAPHY.pptx

macroradiography

1. MACRORADIOGRAPHY Presented by : M.Naga Theja 210513003 M.Sc.Radio-Imaging Technology 1st year

2. Table of Content What is macroradiography ? Principles of macroradiography Magnification factor Factors affecting image quality Geometric unsharpness X-ray tube rating Photographic unsharpness Scattered radiation Aim & applications of macroradiography References Questions

3. What is Macroradiography ? Macroradiography is a radiographic imaging technique used to increase the size of the image relative to the object. In 1982 an Italian doctor named Alessandro Vallebone proposed this technique.

4. Principles of Macroradiography. A technique of producing an image by direct magnification using an x-ray tube with very fine focal spot. Focal spot-object distance will be adequatly changed in accordance with the change in accordance with the change in magnification.

5. [Cotd…] Magnified image can be produced by increasing the object to film distance from the point source. The required magnification is obtained by moving the object away from the film.

6. [Cotd…] However, the geometric unsharpness increases with the increase of magnification.

7. Magnification Factor The ratio of image size to object size is known as magnification factor. Its value is normally assessed by measuring the focus - film distance (FFD) and the object - film distance (OFD). the focus - object distance (FOD) is then obtained by subtraction: FOD = FFD - OFD Thus , Magnification factor = FFD/FFD-OFD=FFD/FOD

8. [Cotd…] For a routine examination of the hand (dorsipalmar projection), the relevant dimensions are typically: FFD = I 00 cm, OFD = I cm. This gives a magnification factor of 100/99 = 1.01. Thus, a 10 cm long finger gives an image which is 10.1 cm in length. For a lateral projection of the lumbar spine, the relevant dimensions arc typically: FFD = I 00 cm, OFD = 25 cm (spine-table-top distance + table-top-film distance). This gives a magnification factor of 100/75 = 1.3. A true measurement of 10 cm in the spine is reproduced as 13 cm in the image

9. [Cotd…] For macroradiography, it is usual to arrange the FFD and OFD to give a magnification factor of at least 1.5. Typically, a magnification factor of2.0 is achieved by positioning the structure under examination half-way between the X-ray tube focus and the film, i.e. FFD = FOD x 2 (sec Fig. 26.2). In practice, the FOD is often maintained at its normal value but the FFD is increased, i.e. the X-ray tube and patient are positioned normally hut the film is moved further from the patient.

10. Factors affecting Image Quality The quality of the magnified image is also an important consideration, which may be affected by modifications to the FFD, FOD and OFD. Geometrical factors involves, Geometric Unsharpness X-Ray tube rating Photographic Unsharpness Scattered radiation

11. Geometric Unsharpness Geometric unsharpness refers to the loss of sharpness of feature on radiograph that correspond to the boundaries from thickness that result of geometric factor of the radiographic equipment and setup. To reduce this the the point source focal spot used.

12. In the 1st image, radiation originates at a very small source, so very little geometric unsharpness is produced in the image. In the 2nd image, the source is large & different path the rays of radiation can take from their point of origin in source that cause the edges of the notch to be less defined. Source Film Film density plot

13. Formulae of Geometric Unsharpness When the detector is not placed next to sample, such as when the geometric magnification is used then, Ug = f . b/a f = Source focal spot a = Subject - Source distance b = Subject - detector distance Source focal spot Subject Detector Penumbra {Ug}

14. X_Ray Tube rating To limit geometric unsharpness and still achieve substantial magnification requires the use of an ultrafine focus. Such a small focus sets serious constraints on the output of the X-ray tube. This may well be manifested as a reduction in maximum tube current e.g. from over 1000 mA on broad focus to less than 400 mA when fine focus is selected, and consequently, exposure times become longer than desirable. Unless great care is taken, motional unsharpness is the result. Motional unsharpness problems can be alleviated by: Taking positive measures to immobilize the patient; Using fast film-screen systems, if necessary

15. [Contd…] E xtremities is often highly successful because the required X-ray exposure is small and effective immobilization is possible: thus, high-resolution screens can be used. Macroradiography may prove impossible, e.g. for many abdominal structures the large exposures necessary and the problems of involuntary movement may exclude macroradiography as a viable technique. minimizing the FFD may ease rating problems but the radiographer must be alert to the increased radiation dose to the patient associated with a short focus-skin distance.

16. Photographic Unsharpness T he resolution of the film or film-screen system is not normally a critical limiting factor in carrying out macroradiography. Photographic unsharpness ( Up) remains constant because it is not the recorded image that is magnifie d.

17. Scattered Radiation The large object-film distance used in macroradiography reduces the amount of forward-scattered radiation reaching the film from the patient. It is not necessary to use a secondary-radiation grid, even for regions such as the skull or spine where a grid would be essential. Collimation of the X-ray beam and provision of backscatter protection for the film help to maintain optimum contrast on the macroradiograph.

18. Aim of Macroradiography. Aimed to improve the study of the bony structures and the pulmonary designs. Allows the small detail obvious in the image. Application of Macroradiography Carpal bones of the wrist (especially the scaphoid bone) Bones of hand, e.g., early detection of metabolic bone disease. Temporal bone. The lacrimal system during D acryocystography . Nodular pattern in chest radiographs. Cerebral Angiography.

19. References Macroradiography using conventional radiography. https://doi.org/10.1259/bjr.75.898.750831 Chesney's Radiographic Imaging 6th edition

20. Questions ? Whats are the 2 requirements of successful macroradiography ? How is macroradiography is achieved ? What is the main disadvantage of macroradiography ? What is the formulae of geometric unsharpness ? Who proposed macroradiography ?